Nicotinic signaling is widespread in the nervous system and influences numerous behaviors and neuropathologies. The signaling depends on nicotinic receptors which often promote calcium influx and regulate calcium-dependent events. The consequence of signaling, therefore, can depend critically both on receptor location and on the identity of associated intracellular components. Recently it has been shown that members of the PSD-95/SAP90 family form a postsynaptic PDZ-scaffold associated with nicotinic receptors on neurons. The scaffold not only helps mediates downstream signaling but also plays an important but unknown role in supporting synaptic input to the neuron. Preliminary results suggest that postsynaptic neuroligin, EphB2 receptors, and rapid activity-driven SNARE-dependent receptor trafficking also converge in the postsynaptic neuron to regulate nicotinic signaling. Four specific aims are proposed to pursue these findings: (1) Determine how postsynaptic PDZ-scaffolds influence synaptic input and identify possible intermediate components exerting the effect. (2) Test the hypothesis: that postsynaptic neuroligin supports nicotinic input independently from PDZ-scaffolds and determine how it interacts with nicotinic receptors. (3) Examine the mechanisms promoting rapid trafficking of nicotinic receptors on neurons and assess their physiological significance for synaptic signaling. (4) Test the hypothesis that EphB2 receptors enhance nicotinic effects and examine the interdependence of convergent pathways controlling nicotinic signaling in neurons. Fluorescence imaging will be used to visualize synaptic components; transfections will be used to manipulate interacting partners; electrophysiological analysis will be used to study functional consequences; and biochemical and molecular biological techniques will be used to probe interactions. Experiments will focus mainly on chick ciliary ganglion neurons but will also employ transfected cell lines to define molecular interactions, and rat hippocampal neurons to assess the generality of the findings. These results will provide new insight into regulatory mechanisms that shape nicotinic signaling, important because the signaling is pervasive and has profound biomedical consequences.